Alzheimer's disease (AD) is a progressive dementing disorder of the elderly characterized by a series of structural abnormalities of the brain. Neurons in multiple regions of the central nervous system (CNS) become dysfunctional and die, resulting in alterations in synaptic inputs. Cell bodies and proximal dendrites of these vulnerable neurons contain neurofibrillary tangles composed of paired helical filaments, the main component of which is a phosphorylated microtubular-binding protein, namely tau. One of the hallmarks of the disease is the accumulation of amyloid containing deposits within the brain called senile (or neuritic) plaques. The principal component of amyloid plaques is β-amyloid peptide (hereinafter “BAP,” also referred in the literature as Aβ, βAP, etc.), which forms dense aggregates during the course of AD.
BAP is a 39–43 amino acid peptide derived by proteolytic cleavage of amyloid precursor protein (hereinafter “APP”) and composed of a portion of the transmembrane domain and the luminal/extracellular domain of APP. It is thought that the BAP peptide comprising 42 amino acids (BAP42) is potentially the more toxic aggregated form in humans. APP occurs as several BAP-containing isoforms. The major forms are comprised of 695, 751, and 770 amino acids, with the latter two APP containing a domain that shares structural and functional homologies with Kunitz serine protease inhibitors. In normal individuals, BAP does not accumulate and is rapidly removed from circulating fluids. However, the peptide can form plaques on surfaces of dystrophic dentrites and axons, microglia, and reactive astrocytes. The aggregation and deposition of BAP in neuritic plaques is postulated as one of the initiating events of AD. Investigation of the events leading to the expression and consequences of BAP and their individual roles in AD is a major focus of neuroscience research. In particular, the discovery of proteins that bind to BAP is critical to advance understanding of the pathogenesis of the disease and to potentially introduce novel therapeutic targets.
Until the present invention, proteins and fragments thereof that bind with human BAP and that may be involved in the biological effects of BAP in AD had not been identified.